In wireless communication network the format in which the data is communicated between network nodes is transmitted as control information in a specified and known way. The receiving node, which might, for example, be a UE in a LTE network, first decodes the control information, which may be a grant, that contains information on the transport format of the transmitted downlink data or the data to be transmitted, uplink data. A particular example of the formatting information is the allocation, that is, where the data is located, typically in frequency. Another example relates to the number of layers used, still another example relates the modulation and coding information. In LTE networks, the grant is transmitted on PDCCH or ePDCCH using a variety of DCI formats which are specific to different operating modes of the UE. For example, in the random access procedure the eNB when sending a random access response to the UE the eNB uses DCI format 1A. The eNB uses this format since this is known to all UEs and the eNB does not know the actual capabilities of the UE when sending the random access response. Later in the call setup procedure the eNB learn the UE capabilities and can start using a more advanced DCI format. A grant received on PDCCH/ePDCCH is relative a specific subframe (except semi-persistent grants that are relative multiple subframes), wherein for downlink, DL, grant specific to same subframe n in which the grant was detected while for uplink, UL, grants is specific to a future subframe n+a, where usually a=4.
In legacy state-of-the art systems such as LTE the physical downlink control channel, also referred to as PDCCH, supports multiple formats and the format used is a priori unknown to the terminal. Therefore the terminal needs to blindly detect the format used on the downlink control channel in order to receive the downlink control information, DCI. In addition the PDCCH is a shared channel in which several terminals can be scheduled in the same transmission time interval, TTI, and the UE/wireless device does not a priori know where in the PDCCH it will find the DCI.
The theoretical maximum amount of blind decoding attempts that would be needed for a terminal to find any possible DCI of any size and location is typically much larger than the number of blind decoding attempts that the terminal is capable of performing in a TTI. Hence it is required to have mechanisms that limit possible DCI sizes and location that the terminal is supposed to monitor. Clearly, from a scheduling point of view, restrictions on how the PDCCH may be used are undesirable and may influence the scheduling flexibility and impose additional processing at the transmitter side. At the same time, requiring the terminal to monitor all possible DCI locations and sizes is not attractive from a terminal complexity point of view.
To impose as few restrictions as possible on the scheduler while at the same time limit the maximum number of blind decoding attempts in the terminal, LTE defines so called search spaces which describe where in the downlink control channel the terminal is supposed to monitor for downlink control information.
To clarify, it is possible to consider such a search space as a set of candidate control channels formed by for examples CCEs, control channel elements, on a specified aggregation level. Allocation of resources may thus be performed by means of such CCEs, control channel elements. The allocated or assigned search space is supposed to be decoded by a terminal, or a wireless device, in order to obtain downlink control information. There exist in general multiple aggregation levels, corresponding to two, four and eight CCEs, and it therefore exist multiple search spaces for each terminal or wireless device. The terminal attempts, in each sub-frame and for each search space, to decode all PDCCHs that can be formed from the CCEs. Therefore, if the CRC is valid for a blind decoding attempt the corresponding control channel is also considered valid for the terminal or wireless device and the terminal or wireless device will process the corresponding information. This information will in general concern scheduling information such as scheduling assignments, scheduling grants and alike. An efficient utilization of CCEs makes use of terminal specific search spaces at each aggregation level, that is, a search space specifically allocated to a particular terminal or wireless device. In several situations there is also a need to address a group of terminals in the system and for this purpose LTE has defined common search spaces in addition to the terminal specific search spaces. Common search spaces are for example used when scheduling system information valid for all terminals in the system while terminal specific search spaces are typically used to communicate downlink assignment and uplink grants.
Despite the efforts already made for providing an efficient and flexible scheduling there still exists a need for improvements that could provide even better flexibility as well as a faster way of identifying and decoding relevant control information. If it would be possible to provide mechanisms whereby a wireless device is provided with means to, e.g., more quickly identify relevant control information, this would in turn free a lot a transmit resources which would enable a more efficient use of physical channels for data transmissions. This would ultimately improve the overall throughput of the network system. The proposed technology aims to provide such mechanisms.